Device and method for supplying the triggering device of an occupant restraint system with power

ABSTRACT

The invention relates to a device that comprises a plurality of energy stores and a driver circuit. Said driver circuit is supplied by at least two of the energy stores via a selecting circuit in such a manner that the driver circuit is always supplied by the energy store that has the highest voltage as compared to the remaining energy stores.

CLAIM FOR PRIORITY

This application claims priority to International Application No.PCT/DE01/01619 which was published in the German language on Dec. 6,2001.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a device and a method for supplying power to afiring means of a vehicle-occupant restraint system.

BACKGROUND OF THE INVENTION

What are referred to as electric firing circuits form the essentialcomponent of a controller for vehicle-occupant restraint systems, forexample airbag controllers. Such firing circuits contain, as theiressential component, at least one firing cap which causes the airbagpropellant to explode when firing occurs by supplying electrical energy.Further components or at least two electronic switches which arefrequently implemented as part of a customized circuit, for example inthe form of a MOS field-effect transistor. The switches which areusually opened are closed when the respective airbag is fired, by meansof a control signal which is correspondingly adapted by a driver circuitfor controlling the switches (MOS field-effect transistor). Theelectronic switches have, in the connected-through state, an electricalcontact resistance which is, inter alia, a function of the gate voltageof the respectively used MOS field-effect transistor. In order toachieve low power losses it is favorable to keep the contact resistanceduring the firing to a minimum. However, for this purpose the gatevoltage of the MOS field-effect transistor must be as high as possible.This factor in itself requires the supply voltage of the driver circuitfor the electrical circuits to be kept high for as long as possible, thesupply voltage then being several volts above the firing voltage.

For this reason, a switching regulator which increases the batteryvoltage of the vehicle to the level of the firing voltage is usuallyprovided in the airbag controller. A step-up converter, which has acapacitor (preferably electrolytic capacitor) for smoothing theswitching voltage and for buffering the energy necessary to operate acontrol device (ECU), is usually used to step up the voltage. The energyreserve stored in the capacitor (acting as an energy store) is fed via adiode to a charge pump whose output voltage is several volts higher thanthe firing voltage. The voltage which is stepped up by the charge pumpis then used to supply the driver circuit for the switches.

However, energy is removed from the energy store (capacitor) during thefiring process and, as a result, the voltage across the energy storedrops. This can lead to a situation in which sufficient voltage toensure complete through-connection of the MOS field-effect transistorsis no longer available. As a result of this, under certain circumstancesthe firing process can in turn only be carried out incompletely, whichitself can lead to faults in the overall functioning of the airbag.

SUMMARY OF THE INVENTION

The invention improves the through-connection of the power supply of avehicle-occupant restraint system.

In one embodiment of the invention, alongside the energy store at leastone further energy store is additionally made available in the step-upconverter in a controller for a vehicle-occupant restraint system.During the firing of the firing means (firing caps), the various energystores are loaded to differing degrees so that the voltages at theindividual energy stores drop at different speeds. According to oneembodiment of the invention, the driver circuit is supplied via aselector circuit from at least two such energy stores such that thedriver circuit is always supplied from the energy store with the voltagewhich is the highest in relation to the remaining energy stores. Thismeasure ensures that the highest voltage is always used to supply thedriver circuit so that the driver circuit is supplied in an optimum wayusing the means available. A further advantage is that if an energystore is already loaded by the firing process, and its voltage thussinks, this store is not yet additionally loaded with supplying thedriver circuit.

In another embodiment, it is possible, for example, for a switchingdevice which connects the energy store with the respective highestvoltage to the driver circuit to be provided as the selector circuit.However, a diode matrix is preferably used as it requires a small outlayin terms of circuitry and provides a high level of operationalreliability.

For example, the energy stores in the firing circuits of front airbagsof the vehicle-occupant restraint system and/or in the firing circuitsof side airbags of the vehicle-occupant restraint system and/or in astep-up converter for generating a firing voltage for thevehicle-occupant restraint system and/or in a step-up converter forgenerating a supply voltage for the control device are used as suitableenergy stores, a single step-up converter being preferably used both togenerate the firing voltage and to generate the supply voltage. As aresult, energy stores which are already present in the system are usedso that the efficiency of the overall system is increased, and in theprocess the outlay in terms of circuitry can be kept low.

In order to be able to generate a sufficient high drive voltage when MOSfield-effect transistors are used as switches, in particular ashigh-side switches, in one embodiment of the invention the drivercircuit is supplied from the energy stores via a charge pump. For thispurpose, a charge pump is connected between the selector circuit and thesupply lines of the driver circuit.

In one aspect, the charge pump can have a further energy store forbuffering energy and thus increasing the reliability of supply.

In another aspect, capacitors, and in particular electrolytic capacitorsor gold capacitors owing to their high capacitances, are used as energystores. In this context, capacitors have a relatively favorableprice/capacitance ratio in comparison to other energy stores. However,specific types of accumulator batteries, for example polymer filmaccumulator batteries, can also be applied.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference tothe exemplary embodiments illustrated in the FIGURE.

FIG. 1 illustrates a firing device in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the firing device which is shown as an exemplary embodiment, anairbag (not illustrated) is fired when necessary by means of a firingcap 1. The firing cap is connected to a firing voltage by means of twoMOS field-effect transistors 2 and 3 which are used as controlledswitches, it being possible to tap the firing voltage to a firingcapacitor 5 by means of a diode 4. For this purpose, the firing cap 1 isconnected via the drain-source path of the MOS field-effect transistor 2to a terminal of the firing capacitor 5 which is connected to areference potential 6, and on the other hand to the other terminal ofthe firing capacitor 5 with intermediate connection of the drain-sourcepath of the MOS field-effect transistor 3 and of the diode 4. The firingcapacitor 5 is fed by a step-up converter 7 which includes a storagecapacitor 8. The firing voltage 8 which is provided both for firing thefiring cap (in conjunction with firing capacitor 5) and for operating acontrol device 9 in the present exemplary embodiment, can be tapped atthe storage capacitor 8. The control device 9 controls a driver circuit10 as a function of a signal 11 of a crash sensor (not illustrated inthe drawing). The driver circuit 10 is finally coupled to the gateterminals of the MOS field-effect transistors 2 and 3 in order toconnect them through when necessary in accordance with the driving bythe control device 9.

In the exemplary embodiment, the two MOS field-effect transistors 2 and3 are preferably of identical design so that the MOS field-effecttransistor 3 correspondingly forms a high-side switch. In order toconnect this transistor through sufficiently, a voltage is necessarywhich is greater than the firing voltage present at the firing capacitor5 and the control device 9. For this reason, the driver circuit 10 issupplied by a charge pump 12. The charge pump 12 increases a voltagepresent at its input by a specific amount. In the exemplary embodimentthe input voltage is approximately doubled in this context.

In particular, the present charge pump 12 comprises a capacitor 13 whichis connected on the one hand to the input of the charge pump 12 and onthe other hand to a node point. The node point is coupled here on theone hand to an auxiliary voltage 15 via a resistor 14 and to thereference potential 6 via the collector-emitter path of a bipolartransistor 16. The bipolar transistor 16 is driven by means of asquare-wave generator 17 so that the bipolar transistor 16 iscontinuously switched on and off. The input of the charge pump 12 iscoupled to its output via a diode 18 in the conducting direction, theoutput being connected to the reference potential 6 via a storagecapacitor 19. The voltage at the input of the charge pump 12 is madeavailable by a selector switch 20. The selector switch 20 includes adiode matrix with three individual diodes 21, 22 and 23 which areconnected in the conducting direction and are at the same time connectedrespectively to an energy store at the input end and to one another atthe output end.

In addition to the storage capacitor 8 of the step-up converter 7, thestorage capacitors 24 and 25 of a front airbag controller 26 and of aside airbag controller 27 are also provided as energy stores.

As a result, the airbag controller (ECU) in the present exemplaryembodiment has a total of at least three energy reserves, namely thereserve of the step-up converter 7, the energy reserve of the frontfiring circuit (front airbag controller 26) and the energy reserve forthe side firing circuit (side airbag controller 27) and if appropriatethe reserve of the charge pump. If the voltage of the step-up converter7 collapses during an impact owing to the connections of the car batterybeing torn off while at the same time the front airbags are fired, thedriver circuits of the firing circuits can be fed from the side energyreserve which is not loaded and which can keep its voltage virtually atthe initial firing voltage.

1. A device for supplying power to a firing unit of a vehicle-occupant restraint system, comprising: a plurality of switches formed as MOS transistors having gate terminals; a plurality of energy storage devices; a control device; a driver circuit for the vehicle-occupant restraint system, the driver circuit coupled to the gate terminals of the MOS transistors; a selector circuit supplying the driver circuit with a voltage from one of the energy storage devices that is higher than a voltage of any other one of the energy storage devices; and a charge pump connected between the selector circuit and the driver circuit.
 2. The device according to claim 1, wherein the selector circuit includes a diode matrix.
 3. The device according to claim 1, wherein: one of the energy storage devices is a part of a firing circuit of a front airbag of the vehicle-occupant restraint system.
 4. The device according to claim 1, wherein: one of the energy storage devices is a part of a firing circuit of a side airbag of the vehicle-occupant restraint system.
 5. The device according to claim 1, further comprising: a step-up converter for generating a firing voltage for the vehicle-occupant restraint system; the step-up converter including one of the energy storage devices.
 6. The device according to claim 1, further comprising: a step-up converter for generating a supply voltage for the control device; the step-up converter including one of the energy storage devices.
 7. The device according to claim 1, wherein the charge pump includes an energy storage device.
 8. The device according to claim 1, wherein the energy storage devices are capacitors.
 9. A method for supplying power to a firing unit of a vehicle-occupant restraint system, comprising: using switches to feed energy to the firing unit from a first storage device, the switches being MOS transistors having gate terminals; providing a driver circuit for actuating the MOS transistors and coupling the driver circuit to the gate terminals of the MOS transistors; using a selector circuit to supply the driver circuit with a voltage from one of the energy storage devices that is higher than a voltage of any other one of the energy storage devices. 